During synaptic plasticity and memory storage, intracellular signaling processes are rapidly activated by the action of neurotransmitters on ionotrophic and metabotrophic receptors. These intracellular signaling pathways in turn alter neuronal function, rapidly changing levels of intracellular calcium and cAMP, thereby activating kinases and inducing new protein synthesis and new gene expression. Despite the rapid temporal nature of the biochemical mechanisms underlying memory storage, the genetic and pharmacological tools used to manipulate these processes in vivo have poor temporal resolution. Gene knockouts result in the loss a gene for the entire lifetime of an organism, regulated transgenic expression or conditional knockouts act over the time course of days and pharmacological reagents often lack the cell specificity needed to manipulate signal transduction pathways selectively in neurons. In this application, we propose to use novel genetic techniques to transiently enhance neuronal cAMP levels in a temporal and spatially restricted manner not previously possible, using heterologous G protein coupled receptors and light-sensitive adenylyl cyclase. In Specific Aim 1, we will use transgenic mice expressing the Aplysia octopamine receptor in forebrain neurons to define the role of neuronal cAMP signaling in learning and memory. By activating this G alpha s coupled heterologous receptor in specific brain regions at specific times during memory storage, we will define when and in what brain regions activation of the cAMP signaling pathway enhances memory. Using biochemical, pharmacological and genetic approaches, we will define the targets of cAMP critical for memory enhancement. Synaptic plasticity, the experience-dependent change in the strength of synaptic connections between neurons, is a cellular model of memory storage. In Specific Aim 2, we will use transgenic mice expressing the Aplysia octopamine receptor to define the molecular mechanisms by which cAMP signaling enhances synaptic plasticity and synaptic tagging. The cAMP signaling pathway also plays a critical role in memory storage in the fruit fly, Drosophila. In Specific Aim 3, we will develop optogenetic techniques using the photo-activatable adenylyl cyclase to manipulate cAMP dynamics in the fly brain in the range of milliseconds using light and will define the role of cAMP signaling in distinct memory phases. The development of novel genetic approaches to rapidly modulate intracellular signaling processes in vivo promises to provide novel insight into mechanisms of memory enhancement.